OnAttributeHttpActionFilters

	using System;
	using System.Collections.Concurrent;
	using System.Collections.Generic;
	using System.Collections.ObjectModel;
	using System.Linq;
	using System.Reflection;
	using System.Web;
	using System.Web.Http.Controllers;
	using System.Web.Http.Filters;

	public interface ICache<in T, out TOut>
	{
		TOut Get(T key);
	}

	public class Cache<T, TOut> : ICache<T, TOut>
	{
		private readonly Func<T, TOut> _populator;
		public readonly ConcurrentDictionary<T, TOut> _cache;

		public Cache(Func<T, TOut> populator, IEqualityComparer<T> comparer )
		{
			_populator = populator;
			_cache = new ConcurrentDictionary<T, TOut>(comparer);
		}

		public TOut Get(T key)
		{
			return _cache.GetOrAdd(key, _populator);
		}
	}


	public class ActionDescriptorComparer : EqualityComparer<HttpActionDescriptor>
	{
		public override bool Equals(HttpActionDescriptor x, HttpActionDescriptor y)
		{
			return x.ActionName == y.ActionName && x.ControllerDescriptor.ControllerType == y.ControllerDescriptor.ControllerType;
		}

		public override int GetHashCode(HttpActionDescriptor obj)
		{
			return 1; // do this properly
		}
	}


	public class MyAttribute : Attribute
	{
		public string SomeValue { get; set; }
	}


	public class OnAttributeAttribute<TOut> : ActionFilterAttribute
	{
		private readonly ICache<HttpActionDescriptor, TOut> _cache;
		private readonly Action<TOut> _action;

		public OnAttributeAttribute(ICache<HttpActionDescriptor, TOut> cache, Action<TOut> action)
		{
			_cache = cache;
			_action = action;
		}

		public override void OnActionExecuting(HttpActionContext actionContext)
		{
			_action(_cache.Get(actionContext.ActionDescriptor));

			base.OnActionExecuting(actionContext);
		}
	}

	public static class DumpingGround
	{
		public static Collection<MyAttribute> GetMyAttribute(HttpActionDescriptor actionDescriptor)
		{
			return actionDescriptor.GetCustomAttributes<MyAttribute>(true);
		}

		public static void DoSomething(Collection<MyAttribute> attributes)
		{
			Console.WriteLine("hello");
		}

		public static void Main()
		{
			var globalAction = new OnAttributeAttribute<Collection<MyAttribute>>(
				new Cache<HttpActionDescriptor, Collection<MyAttribute>>(GetMyAttribute, new ActionDescriptorComparer()),
				DoSomething);

			//Add globalAction to global filters.

			//Add MyAttribute ( or any other to an action )
		}
	}